Both high density and lower density integrated circuits are fabricated on wafers utilizing numerous fabrication techniques, including, but not limited to, photolithography, masking, diffusion, ion implantation, etc. After the wafers are fabricated, with the wafer including a plurality of integrated circuit dies, a die coat is commonly used to protect the plurality of integrated circuit dies from damage during the remainder of the manufacturing process. It is commonly known to use polyimides as the buffer or die coat when fabricating such devices or wafers.
Polyimides utilized as a spin-on die coat are somewhat expensive. Typically, conventional processes for applying a die coat require about 5 grams of die coat polymer per wafer. When one considers the volume of wafers processed over, for example, one year, this is a significant amount of material and a significant part of the cost of processing. What is needed is a way to reduce the amount of die coat polymer used without significantly impacting process latitudes. One reason retaining process latitudes is important is because wafer-to-wafer repeatability is enhanced by wider process latitudes.
The goal of the coating step is to produce a generally uniform, adherent, defect-free polymeric film of desired thickness over the entire wafer. Spin coating is by far the most widely used technique to apply such films. This procedure is carried out by dispensing a liquid die coat polymeric composition onto the wafer surface, and then rapidly spinning the wafer until the die coat is distributed over the entire wafer surface.
The spin coating procedure begins with dispensing the polymeric composition onto the wafer. The dispensing stage could be accomplished by flooding the entire wafer with polymeric composition (requiring much more than 5 grams of material per wafer), or by dispensing a smaller volume of polymeric composition at the center of the wafer. The wafer is then brought to a constant spin speed to distribute the composition evenly over the wafer surface. During conventional processing, the wafers are typically subjected to an intermediate ramp spin speed followed by a final spin speed. Film thickness typically depends on the viscosity of the solvent-containing liquid polymeric composition and the final spin speed and time duration of the spin. Once the die coat polymeric composition is distributed, edge bead removal solution is added to the wafer and spun to remove excess die coat material from the wafer. Immediately following the application of the die coat material and the bead removal solution, the wafer is dried or “softbaked” by a heat source such as a hotplate.